github-actions[bot] commented on code in PR #65703:
URL: https://github.com/apache/doris/pull/65703#discussion_r3594262435
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fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/eageraggregation/EagerAggRewriter.java:
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@@ -156,10 +156,15 @@ public Plan visitLogicalJoin(LogicalJoin<? extends Plan,
? extends Plan> join, P
Plan newLeft = join.left();
Plan newRight = join.right();
- if (leftChildContext.isPresent()) {
+ // Scalar (GROUP BY empty) child aggregate: returns 1 NULL row even on
0 input rows (SQL standard).
+ // If pushed below a join, that 1 row would cross-join with the other
side, producing phantom rows.
+ // Forbid pushdown when the child aggregate has no GROUP BY keys.
+ // Note: parent scalar aggregates are already filtered at
PushDownAggregation before reaching here.
+ // See regression test: scalar_agg_pushdown.groovy
+ if (leftChildContext.isPresent() &&
!leftChildContext.get().getGroupKeys().isEmpty()) {
Review Comment:
This guard is evaluated before later context rewrites, so it does not
prevent every scalar partial aggregate. A reachable reduced tree after constant
propagation is:
```text
Aggregate(group=[k], sum(z))
CrossJoin
Project(1 AS k, A.v + B.v AS z)
InnerJoin(A.id = B.id)
Scan A
Scan B
Scan R
```
`ConstantPropagation` intentionally retains `k` when it is the only constant
group key, so this check passes. `createContextFromProject` then maps `k` to
the literal's empty input-slot set and `sum(z)` to `sum(A.v + B.v)`. That
aggregate spans both inner-join children, so `visitLogicalJoin` falls back to
`genAggregate` with `groupKeys=[]`. If the inner join is empty, the scalar
partial emits one row and the outer cross join produces a phantom group,
whereas the original tree produces no rows.
Please reject an empty key list at `genAggregate` (or another actual
aggregate-creation boundary). That placement also preserves safe paths where
`visitLogicalFilter` adds keys after this point; this early return currently
disables those valid reductions.
##########
regression-test/suites/query_p0/eager_agg/scalar_agg_pushdown.groovy:
##########
@@ -0,0 +1,54 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+suite("scalar_agg_pushdown") {
+ sql "set eager_aggregation_mode=1;"
+ sql "set eager_aggregation_on_join=true;"
+ sql "set disable_nereids_rules='SALT_JOIN';"
+
+ // Test: scalar aggregation (no GROUP BY) must not be pushed below a join,
+ // because scalar agg on empty input returns 1 NULL row (SQL standard),
+ // which would be cross-joined with the other side to produce phantom rows.
+ // Regression test for: scalar agg pushdown producing phantom rows when
+ // constant propagation replaces GROUP BY key with a literal that doesn't
+ // exist in the table.
+
+ sql """drop table if exists t1;"""
+ sql """create table t1 (a int, b int) distributed by hash(a)
properties("replication_num" = "1");"""
+ sql """insert into t1 values (1,10),(2,20);"""
+
+ sql """drop table if exists t2;"""
+ sql """create table t2 (c int) distributed by hash(c)
properties("replication_num" = "1");"""
+ sql """insert into t2 values (1),(2);"""
+
+ // WHERE t1.a = 999 matches no rows in t1.
+ // GROUP BY includes t1.a, t2.c (cross-table GROUP BY).
+ // Without the fix, eager aggregation pushes a scalar partial aggregate
+ // below the join, which on empty input returns 1 NULL row.
+ // That NULL row cross-joins with t2's 2 rows, producing 2 phantom rows.
+ // With the fix, pushdown is forbidden for scalar child aggregates.
+ qt_scalar_agg_no_pushdown """
+ SELECT t1.a, SUM(t1.b), t2.c
+ FROM t1, t2
+ WHERE t1.a = 999
+ GROUP BY t1.a, t2.c
+ ORDER BY t2.c;
+ """
+
+ sql """drop table if exists t1;"""
Review Comment:
Please remove these trailing drops. The repository test convention is to
drop tables before setup and leave them in place afterward so a failed run can
be inspected; lines 30 and 34 already provide the required cleanup.
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